In the conventional technique, host (such as computers, mobile phones, etc.) sequentially issues commands one by one to electrically-coupled storage device (such as flash memory, etc.); and correspondingly, the storage device executes corresponding tasks (such as write, read, etc.) according to the sequence of the commands transmitted from the host. However, in this conventional operation manner, the storage device must execute tasks according to the sequence arranged by the host. Thus, once a task has a relatively-long execution time, the following other tasks have to wait; and consequentially the task execution efficiency may be relatively low.